1. Field of the Invention
The present invention relates to a scanning technique of an LCD (liquid crystal display) panel. More particularly, this invention relates to an LCD module with symmetrical scanning circuit boards at the two ends of the LCD panel.
2. Description of the Related Art
FIG. 1 (Prior Art) is a plane view of a conventional LCD module. As shown in FIG. 1, the LCD module comprises an LCD panel 100, a data circuit board 120, a plurality of data driver integrated circuits (ICs) 122, a scanning circuit board 130, a plurality of scan driver ICs 132, and a driving circuit 110. Driving circuit 110 connects to data circuit board 120 via connecting line 112 for transferring corresponding data driving signals and scanning control signals. Data circuit board 120 then connects to scanning circuit board 130 through connector 125 for transferring scanning control signals to scanning circuit board 130. Data driver IC 122 and scan driver IC 132 are in the form of the tape carrier package (or called TCP). Data driver ICs 122 connect to data circuit board 120 at the upper part of LCD panel 100, and scan driver ICs 132 connect to scanning circuit board 130 at the left side of LCD panel 100. The display of the conventional LCD is achieved by using a back light source or other light sources, which would not be described here.
FIG. 2 (Prior Art) is a circuit diagram of the conventional LCD panel 100. Assume that the LCD panel is a color LCD. As shown in FIG. 2, the LCD panel comprises a pixel electrode 101 with an array of m rows and 3n columns. The number of the pixel electrodes 101 is m×3n. Additionally, each pixel electrode 101 is configured at the intersection of the scanning lines (represented as 102(1)˜102(m)) and the data lines (represented as 103(1)˜103(n)), and the scanning lines are controlled with scan driver ICs 132, and the data lines are controlled with data driving ICs 122.
In a color LCD, each pixel comprises three pixel electrodes 101 representing red, green and blue, respectively. Namely, a group of m×n pixel electrodes 101 is used to represent red and forms the R subpixels. Another group of m×n pixel electrodes 101 is used to represent green and forms the G subpixels. Finally, the rest of the m×n pixel electrodes 101 is used to represent blue and forms the B subpixel. As a result, the color LCD has a total pixel or point number of m×3n.
The first to the m-th scanning lines or electrodes 102(1) to 102(m) are respectively aligned along the rows of the array. The first to the 3n-th data lines or electrodes 103(1) to 103(3n) are respectively aligned along the columns of the array. Thus, thin film transistors (TFTs) 106 with a total number of (m×3n) are configured at the intersections of scanning lines from 102(1) to 102(m) and data lines from 103 (1) to 103 (3n), in order to drive each of m×3n pixel electrodes 101.
Each TFT 106 on the same scanning line with its gate electrically links to the corresponding one of the scanning lines from 102(1) to 102(m). And each TFT 106 on the same data line with its drain electrically links to the corresponding one of the data lines from 103(1) to 103(n). The sources of all TFTs 106 electrically link to the corresponding pixel electrode 101.
According to FIG. 1 and FIG. 2, the operation of the conventional LCD module is described below. First of all , according to the current image data, driving circuit 110 sends the data driving signal to data circuit board 120 and sends the scanning control signal to scanning circuit board 130. According to the scanning control signal, scan driver IC 132 is able to scan every scanning line from 102(1) to 102(m) on the LCD panel. That is, scan driver IC 132 sends a logic high level signal to one of the scanning lines to turn on the TFTs 106 connected to this scanning line. On the other hand, data driver IC 122 sends the image data to the data lines from 103(1)to 103(3n). Meanwhile, all TFTs 106 connected to the scanning line pass the image data on the data lines to the correspondent pixel electrodes 101 for displaying. After all the scanning lines from 102(1) to 102(m) are scanned in sequence, the displaying of the whole picture frame is completed.
As described above, while processing the display of the pixels on a specified scanning line, scan driver IC 132 must send a logic high level signal to turn on all TFTs 106 on the scanning line. Accordingly, the image data on the data lines can be sent to the corresponding pixel electrodes 101. However, the case described above is ideal condition. In the real condition, since there is a delay effect caused by RC time constant of the conducting lines, the logic high level signal received by TFTs 106 connecting to the scanning line may undergo a severe distortion. FIG. 3 (Prior Art) is a schematic diagram of a conventional technique of a practical procedure for scanning the scanning lines. The logic high level pulse signal 133a sent from the scan driver IC 132 will turn on the nearest TFT 106 first. Nonetheless, when the logic high level pulse signal is transferred via the scanning line, the high frequency components are filtered out and a logic high level pulse signal 133b is produced due to the RC time constant of the resistance and the capacitance of the conducting line. The distorted logic high level pulse signal 133b could neither insure that the correspondent TFT 106 being provided with sufficient turn-on time to allow the image data to enter pixel electrode 101, nor that the closing time of the previous TFT being fast enough to avoid been overlapped by the next data line. The phenomenon is going to get worse in the LCD modules with larger sizes and higher resolutions. For example, in the LCD with the XGA type (with the size of about 13.3″ to 14.1″, and the resolution of 1024×768), the time for scanning each scanning line is about 20.67 μs. On the other hand, it will take 13.39 ms to scan each scanning line of the LCD with the UGXA type (with the size of 17″, and the resolution of 1600×1200). Hence, when the size and resolution of an LCD get bigger, the delaying problem of the scanning line is getting more serious. This is the problem encountered when proceeding the driving of a conventional LCD module.